同学你好，该知识点来自沪江网校《初级水平直达雅思6.5分【剑桥全能随到随学班】》的课程，想要更系统的学习，欢迎进入课程学习。不仅可以和更多的同学一起学习，而且还有老师、助教随时的学习指导和知识点解答哦。

同学你好~
可以的。第四句可以用wasn't able to

could和be able to

在表示过去的一般能力时，两者没有很大差别。例如：

I could / was able to play the piano when I was young. 我年轻时会弹钢琴。

但如果要表示一时的能力，即在过去某时有某种能力，并顺利地完成某事，则要用 was / were able to，而不能用 could。例如：

Though he was sick, he was able to swim across the river. 虽然他病了，但他还是游过了河。

After five hours of climbing, we were able to reach the top of the mountain. 经过5个小时的攀爬，我们终于登上了山顶。

could 表示可能或有能力做，was [were] able to 则表示能够做且确已做到。比较下面两句：

I was able to pass the examination. 我通过了考试。（不仅有能力，而且实际上做到了。相当于I succeeded in passing the examination.）

I could pass the examination. 我当时有能力通过考试。（有能力，但实际上不一定做得到）

祝同学学习进步~